Analytical Chem Soil HW Solutions 31

Analytical Chem Soil HW Solutions 31 - 31 Q3.3 In the...

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Unformatted text preview: 31 Q3.3 In the constant head permeameter test described in Example E3.2, the sample was found to fluidize in upward flow at a hydraulic gradient of 0.84. Estimate the unit weight of the soil in its loosest state. [University of London 2nd year BEng (Civil Engineering) examination, Queen Mary and Westfield College (part question)] Q3.3 Solution Consider a plug of soil on the verge of uplift (main text Figure 3.24). Neglecting side friction, uplift will just occur when the upward force due to the pore water presure acting on the base (A. γ w .[z+h crit ]) begins to exceed the weight of the block of soil (A. γ .z): A . γ w .[z+h crit ] = A. γ .z z ( γ - γ w ) = γ w .h crit or i crit = h crit /z = ( γ - γ w )/ γ w (main text Equation 3.33) In the present case, i crit = 0.84. Taking γ w = 9.81 kN/m 3 , (9.81 kN/m 3 × 0.84) = g – 9.81 kN/m 3 ⇒ γ = 18.05 kN/m 3 (taking γ w = 10 kN/m 3 gives γ =18.4 kN/m 3 ) Q3.4 An engineer wishes to investigate the bulk permeability of a layered soil comprising Q3....
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